1. Technical Field
The present invention relates to optical data transmission systems and methods and more particularly to forward error correction (FEC) in optical systems at data rates at or above 100 Gb/s.
2. Description of the Related Art
Stochastic arithmetic was introduced in 1960's, as an option for the implementation of low-precision digital circuits. Because the optical signal transmission at 100 Gb/s and above is severely deteriorated by impact of intrachannel nonlinearities and polarization-mode dispersion (PMD), the use of forward error correction (FEC) is of great importance.
There are two approaches proposed so far. In a first approach, it has been proposed to use a generalized low-density parity check (LDPC) codes with component Reed Solomon (RS) codes. This scheme provides excellent coding gains, but it is based on hard-decision decoding, and the decoding latency is high.
In a second approach, the use of LDPC codes with 2 bits precision for soft-decoding has been proposed, but relies on the possibility of analog to digital (A/D) converters operating above 100 Gb/s. This type of converter is no currently available. Moreover, the second approach employs a very simple decoding algorithm which introduces error floor at very low bit error rates (BERs). To solve that problem they had to use an additional RS code as an outer code.